Fourier transform far-infrared spectroscopy of HN₂⁺ on the AILES beamline of synchrotron SOLEIL

We report the pure rotation spectrum of HN₂⁺ as measured by Fourier transform (FT) absorption spectroscopy in the 20-40 cm^-1 spectral range. The cations are produced in a liquid nitrogen cooled hollow cathode discharge cell developed on the AILES beamline of synchrotron SOLEIL. The setup was optimized by recording rotation-vibration spectra of H₃⁺ (with the ν₂ band centered at about 2521 cm^-1), HN₂⁺ (with the ν₁ band centered at about 3234 cm^-1), and HCO⁺ (with the ν₁ band centered at about 3089 cm^-1). Many rotation-vibration lines have been assigned for each ion and five pure rotational transitions have been detected for HN₂⁺. These results demonstrate the feasibility of recording far-infrared spectra of cationic species using FT broad band spectroscopy associated with the bright synchrotron radiation continuum as an alternative to laser-based frequency tunable techniques. (author)